1. Field of the Invention
The present invention relates to a fault diagnostic system for an internal combustion engine and a fault diagnostic method for an internal combustion engine, and particularly relates to a fault diagnostic system for an internal combustion engine and a fault diagnostic method for an internal combustion engine in which a fault diagnosis for an internal combustion engine is performed based on the temperature of cooling water.
2. Description of the Background Art
An engine is known which includes a first water temperature sensor provided for a water jacket of the engine to detect an engine water temperature and a second water temperature sensor provided for a cooling water passage from a radiator to the engine to detect a radiator exit water temperature.
For example, Japanese Patent Laying-Open No. 2000-220454 discloses an engine in which a cooling fan is controlled based on the temperatures detected by the first water temperature sensor and the second water temperature sensor.
However, in the case of performing a fault diagnosis for an engine through use of the engine water temperature detected by the first water temperature sensor and the radiator exit water temperature detected by the second water temperature sensor, accuracy in fault diagnosis for the engine may be degraded if there is mismatch between detection characteristics of the first water temperature sensor and detection characteristics of the second water temperature sensor.
That is, if a detected value of the first water temperature sensor and a detected value of the second water temperature sensor are different even though the engine water temperature and the radiator exit water temperature are identical, accuracy in fault diagnosis for the engine will be degraded due to the difference in detection characteristics between the first water temperature sensor and the second water temperature sensor.